もうこれ以上はないぐらいに is a partial sentence that needs some sort of adjectival phrase to modify. It means something like "couldn't be Y", where Y is an adjective in comparative form. Literally, it means, "it is almost like（くらいに） there is nothing（ない） above （以上）this（これ)", so the phrase as a whole acts like a modifier to make a superlative. Examples: これ以上ないくらい幸せ = (I) couldn't be happier! = 最高に幸せ これ以上ないくらい悪い = (This) couldn't be worse! = 最悪 So to figure out what the full sentence means, we will have to look at the phrase before or after もうこれ以上ないくらいに。

It's hard to say without context, but I would translate it as "It's as though we can't go any further." It's an incomplete phrase and without context, it's difficult to say exactly what is meant, but in general terms, this is how I see it.